Cactusoverwintering:
Almost all cacti need a long
cold winter rest with very limited, if
any, watering to
set flowers.
It is generally accepted that plants
kept at too high a temperature or
watered too much during the winter
rest period will not bloom the following year.
Without this cool winter period (0-10° C) they normally wont get
many buds.
The importance of a
long cool winter rest where water is completely withheld needs to be
highly emphasized with this plants. This are plants which can be at
risk for fungalrot even with the slightest amount of
water during
theirs winter rest. A long winter's rest prepare cacti for the
Off-season.

In the wild some
species cannot tolerate temperatures below 10 C,
other like it best around 5 C and some prefer sleeping under a snow
cover.
The
overwinteringof
cold hardy cacti is a
process in which them
must to dehydrate to survive the cold. They wrinkle up, pulls
themselves down into the soil, turn purple and look like death
warmed over for the rest period. The worse they look, the better
they are doing. Then in spring, they fill back up and look good
again.

In cultivation most
species like cool night time temperatures around
5° C, although a few degrees under zero during a very short period
would not be a problem. But it is not recommend to grow cacti for
long periods below zero as this could damage them. Generally in a
heated greenhouse no water is given for five-six months between
September and April, or between November and March, according to the
climate one live in.
Two other important factors to ensure for plant
health during
overwintering time are sun exposure and
a very good ventilation.